Gilera Runner Standard & Purejet Barrels

I'm wondering what the difference is between the barrels on these two engines.
Visually they seem identical, however, in the ad details, most places state only for Purejet injected engines.
Does anyone know what the difference is, and why the other barrel can't be used on a purejet?

 

Found out today whilst at one of my suppliers that there is no difference in the barrels between these two engines. They both have the same Piaggio part numbers. And the pistons are the same as well, same part numbers.